C. Meier

Photonic bands in two-dimensionally patterned multimode GaN waveguides for light extraction

We observe experimentally by photoluminescence the band structure and specific emission properties of an in-plane, light-diffracting photonic crystal formed onto a multimode gallium nitride waveguide. Clear-cut two-dimensional photonic crystal effects are reported. Comparison with modeling results in identification of the band structure, provides insight into the light diffraction mechanism and points out design issues for enhancement of the extraction efficiency.

Vertically oriented GaN-based air-gap distributed Bragg reflector structure fabricated using band-gap-selective photoelectrochemical etching

A three-period vertically oriented GaN-based air-gap distributed Bragg reflector structure was fabricated using band-gap-selective photoelectrochemical (PEC) etching. The epitaxial structure consisted of an Al0.08Ga0.92N∕(In0.04Ga0.96N∕In0.07Ga0.93N) superlattice structure, wherein the InGaN layers served as sacrificial layers during PEC etching. Microreflectance measurements yielded an average enhancement in the reflected signal of ∼12-fold over the wavelength range of 550–650 nm, when compared with the signal from a dry-etched GaN surface.

GaN blue photonic crystal membrane nanocavities

GaN-based photonic-crystal membrane nanocavities with Q factors up to 800 have been realized at the wavelength of ∼480nm. The tuning behavior agrees well with numerical calculations using the finite-difference time-domain method. Theoretically, the lowest energy mode of a cavity that consists of seven missing holes in the Γ-K direction promises a Q factor as high as 4×104 with a mode volume of about 1.3×(λ∕n)3.GaN-based photonic-crystal membrane nanocavities with Q factors up to 800 have been realized at the wavelength of ∼480nm. The tuning behavior agrees well with numerical calculations using the finite-difference time-domain method. Theoretically, the lowest energy mode of a cavity that consists of seven missing holes in the Γ-K direction promises a Q factor as high as 4×104 with a mode volume of about 1.3×(λ∕n)3.

Free-standing, optically pumped, GaN∕InGaN microdisk lasers fabricated by photoelectrochemical etching

GaN-based, mushroom-shaped microdisk lasers were fabricated using band-gap selective photoelectrochemical etching. The optically pumped microdisks had well-defined, distinct modes at excitation powers ranging from about 8to16W∕cm2. Modal linewidths of 0.09nm were reported, which was near the resolution of the measurement equipment. Quality factors for the microdisks were >4600. The observed lasing threshold was 12.1W∕cm2. At higher excitation powers, heating effects and degradation were observed in the optical response of the microdisks.

Frequency control of photonic crystal membrane resonators by monolayer deposition

We study the response of GaAs photonic crystal membrane resonators to thin-film deposition. Slow spectral shifts of the cavity mode of several nanometers are observed at low temperatures, caused by cryo-gettering of background molecules. Heating the membrane resets the drift and shielding will prevent drift altogether. In order to explore the drift as a tool to detect surface layers, or to intentionally shift the cavity resonance frequency, we studied the effect of self-assembled monolayers of polypeptide molecules attached to the membranes. The 2-nm-thick monolayers lead to a discrete step in the resonance frequency and partially passivate the surface.

Visible resonant modes in GaN-based photonic crystal membrane cavities

Photonic crystal membrane cavities play a key role as building blocks in the realization of several applications, including quantum information and photonic circuits. Thus far, there has been no work on defect cavities with active layers emitting in the UV to green range of the spectrum based on the (Al,In,Ga)N material system. While this material system has great potential for a new generation of optoelectronic devices, there are several obstacles for the fabrication of GaN-based membrane cavities, including the absence of a conventional selective chemical wet etch. Here, we demonstrate the first fabrication of fully undercut GaN photonic crystal membranes containing an InGaN multiquantum well layer, fabricated using band-gap-selective photoelectrochemical etching. A postfabrication coating of Ta2O5 is used to tune the cavity modes into resonance with the quantum well emission, and the fabricated membranes exhibit resonant modes with Q=300.

Synthesis of luminescing (In,Ga)N nanoparticles from an inorganic ammonium fluoride precursor

A mixture of cubic and hexagonal indium gallium nitride nanoparticles was prepared by ammonolysis of the precursor ammonium hexafluoroindate-gallate [(NH4)3In1−xGaxF6]. The particles were characterized by transmission electron microscopy. The ratio of the two obtained phases, as well as their composition, was determined using X-ray diffraction, inductively coupled plasma spectroscopy and energy dispersive X-ray spectroscopy. All methods gave consistent results of ∼10% hexagonal material and ∼90% cubic material. The mixture of cubic and hexagonal indium gallium nitride exhibited photoluminescence in the visible region around 735 nm when excited by a 325 nm HeCd laser at room temperature.

Technique for tilting GaAs photonic crystal nanocavities out of plane

The authors demonstrate a technique to mechanically tilt GaAs membranes out of the substrate plane by an arbitrary angle. Tilting is achieved by dosing a thin line of a perforated membrane with Ga ions using a focused ion beam. The change in material properties at the dosing site initiates a tilt about this axis that is monitored in situ to achieve the desired angle. The authors apply this technique to modify the emission direction of photonic crystal cavity, quantum dot light sources.

Optical properties of GaN Photonic Crystal Membrane Nanocavities

L7 photonic-crystal membrane nanocavities with Q factors of 600 have been realized based on the GaN/InGaN material system. Theoretically, a L7 nanocavity promises high Q factors as high as 5×104.

Optical properties of GaN Photonic Crystal Membrane Nanocavities at Blue Wavelengths

L7 photonic-crystal membrane nanocavities with Q factors of 600 have been realized based on the GaN/InGaN material system. Theoretically, a L7 nanocavity promises high Q factors as high as 5×104.